Method of jacketing telephone cables



Jan. 4, 1966 B. J. COHEN 3,227,786

METHOD OF JACKETING TELEPHONE CABLES Filed Oct. 25, 1962 INVENTOR.

BERNARD J COHEN United States Patent C) 3,227,786 METHOD OF JACKETINGTELEPHONE CABLES Bernard J. Cohen, Yonkers, N.Y., assignor, by mesneassignments, to Anaconda Wire and Cable Company, a corporation ofDelaware Filed Oct. 25, 1962, Ser. No. 233,055 2 Claims. (Cl. 264-95) Myinvention relates to telephone cables and particularly to a method ofjacketing such cables without increasing their capacitance unbalance.

In the manufacture of telephone cables it is necessary to balance thecapacitance of the pairs making up the cable core. For this purposegreat care is taken to have uniform insulation on each wire and to applyappropriate tension during the pair twinning, quadding, and cablingoperations. To make sure that all ope-rations have been conductedsatisfactorily it is customary to perform electrical tests on the cablecores prior to the application of cable jackets. It has been found,however, that cores which conform to all specification requirementsprior to jacketing will sometimes have high capacitance unbalance afterthey are jacketed.

Telephone cables to which my invention is directed comprise a core madeup of pairs and/or quads of copper conductors stranded together, coveredby a core wrapping. The conductors are each covered by a thermoplasticinsulation and a heavy thermoplastic jacket is applied over the coveringof the core. Although it has been known that the thermoplasticinsulations may be damaged by the heat of extrusion of the jacket it hasnot been practicable to cover the cores with thick, heat insulating corewrappings because of the understandable commercial need to keep thediameters and weights at a practical minimum. Instead the jackets areapplied by so called tubing methods while the core coverings are kept asthin as possible. In the tubing method of applying the jacket-s the coretube and die are selected so as to extrude the jacket in the form of atube considerably larger than the cable core and then draw the jacketdown to the core. This is done by advancing the core somewhat fasterthan the jacket is extruded so that the latter necks down over theformer. By the time the jacket comes into contact with the cable it hascooled somewhat and at that point it is immediately submerged into thewater of a cooling trough. This has the effect of abstracting the heatfrom the jacket but it also causes the jacket to shrink and in so doingthe jacket compresses the core and wedges itself into some of thevalleys of the outer pairs, also driving the core covering down intothose valleys.

The compression of the cable jacket thus has the effect of disturbingthe configuration of the pairs relative to each other and the unbalancewhich may have been negligible in the cable core prior to jacketing isfound to have increased to an unacceptable value in the jacketed cable.

I have discovered that if compressed air is introduced into the coretube during the extrusion of the jacket, shrinkage of the jacket can becontrolled to prevent any compression of the cable core with the resultthat no increase in capacitance unbalance will ensue. My methodcomprises the steps of forming a cable core of a plurality of twistedpairs having low capacitance unbalance and extruding an oversizedthermoplastic jacket such as a polyethylene jacket over the core whilesimultaneously introducing pressurized gas under the jacket.

ice

I advance the core at a speed slightly greater than the speed ofextrusion of the jacket so as to draw down the jacket, water-cool thejacket and shrink the jacket by means of said cooling while regulatingthe air pressure so as to have the jacket make contact with the surfaceof the core without compressing the core.

A more thorough understanding of my invention may be gained from a studyof the appended drawing.

In the drawing the figure shows a sectionalized plan view of cable beingjacketed in accordance with the method of my invention.

Referring to the figure a core 11 which comprises a plurality of pairsof telephone conductors is advancing through a core tube 12 into acooling trough 13. The pairs of the core 11 may also be twisted intoquads and my invention has particular relevance to such cores sinceavoidance of capacitance unbalance is more critical for quadded cables.A die 14 surrounds the core tube 12 and a thermoplastic material such aspolyethylene 16 is forced by known extrusion means, not shown, betweenthe core tube 12 and the die 14. An edge 17 of the core tube 12 issubstantially flush with an edge 18 of the die 14 with the result thatthe plastic 16 is extruded in the form of a tube 19 around the core 11.Due to the thickness of the wall of the core tube 12 the tube 19 isspaced from the core 11 leaving an annular space21. The core 11 isadvanced faster than the material 16 is being forced from the die 14with the result that the tube 19 is drawn down to the core and reducedin thickness at the same time. Thus the thickness of the wall of thetube 19 at a point 22 where it leaves the die is greater than itsthickness at a point 23 where it contacts the core 11. At about thispoint 23 the core enters the cooling trough 13 where heat is abstractedfrom the tube 19 and the latter shrinks to its final size to form ajacket 24 on the core 11.

To prevent the jacket 24 from shrinking too tightly so as to compressthe core 11 I introduce air or other pressurized gas into the core tube12 through piping 26 from a supply not shown. To maintain the gaspressure around the core the core tube 12 which has a funnel portion 27is provided with a bushing 28 which has a slide fit over the core 11.The pressure within the core tube 12 can be controlled by means of avalve 29, and in my process the pressure is maintained so as to let thejacket 24 collapse around the core 11 to the extent of contacting thecore around its surface but not enough to permit the jacket to compressthe core or to enter the valleys between the conductors comprising thesame.

I have invented a new and useful process for making telephone cables forwhich I desire an award of letters Patent.

I claim:

1. The method of making a telephone cable having low capacitanceunbalance comprising the steps of:

(1) forming a cable core of a plurality of twisted pairs having lowcapacitance unbalance,

(2) extruding an oversized thermoplastic jacket over said core while (a)simultaneously introducing pressurized gas under said jacket, (b) saidgas entering and remaining between the pairs of said core, (3) advancingsaid core at a speed slightly greater than the speed of extrusion ofsaid jacket so as to draw down said jacket,

3 4 (4) water-cooling said jacket and References Cited by the Examiner(a) shrinking said jacket by means of said cooling, 7 UNITED STATESPATENTS 5 t d g g ig iggijj gas Pressure Sal core 1,933,019 10/1933Laubi 264-95 (6) regulating said air pressure Within said core s0 5 21291,670 8/1942 WHEY et 264-174 as to have said jacket make contact withthe su-r- 2,331,195 10/1943 Jannsen 26495 face of said core, (7) saidgas pressure preventing said jacket from ROBERT WHITE ii Examinershrinking sufliciently to compress said core. ALEXANDER H. BRODMERKEL,Examiner.

2. The method of claim 1 wherein said jacket is 10 polyethylene.

1. THE METHOD OF MAKING A TELEPHONE CABLE HAVING LOW CAPACITANCEUNBALANCE COMPRISING THE STEPS OF: (1) FORMING A CABLE CORE OF PLURALITYOF TWISTED PAIRS HAVING LOW CAPACITANCE UNBALANCE, (2) EXTRUDING ANOVERSIZED THERMOPLASTIC JACKET OVER SAID CORE WHILE (A) SIMULTANEOUSLYINTRODUCING PRESSURIZED GAS UNDER SAID JACKET, (B) SAID GAS ENTERING ANDREMAINING BETWEEN THE PAIRS OF SAID CORE, (3) ADVANCING SAID CORE AT ASPEED SLIGHTLY GREATER THAN THE SPEED OF EXTRUSION OF SAID JACKET SO ASTO DRAW DOWN SAID JACKET,